In the past, methods for preparing perfluoroalkyl iodides by telomerization of tetrafluoroethylene with trifluoromethyl iodide or by deriving from alcohols were commercially used in practice.
However, no commercially acceptable methods have been developed for the preparation of perfluorooligoether iodides of the following general formula (II): ##STR1## wherein Rf is a perfluoroalkyl group having 1 to 10 carbon atoms and letter n is an integer of from 0 to 100, which are useful intermediates for the synthesis of fluoro resins, fluoro rubbers, and fluoro surfactants.
In the prior art, perfluorooligoether iodides are prepared as shown by the following reaction scheme by starting with a perfluorooligoether carboxylic fluoride of the following formula (III), subjecting the reactant to hydrolysis to form a perfluorooligoether carboxylic acid, reacting it with silver oxide to form a perfluorooligoether carboxylic silver salt, and subjecting the salt to pyrolysis in the presence of iodine to thereby form a perfluorooligoether iodide of formula (II) (see Japanese Patent Application Kokai No. 441/1988). ##STR2##
However, several problems must be solved before this process can be commercially practiced. The end product, perfluorooligoether iodide is recovered only in yields of about 70 to 85%. The intermediate or silver salt is often a solid which is difficult to handle. The use of expensive silver necessitates silver recovery from a commercial standpoint. The overall process involves three steps, during which toxic hydrogen fluoride evolves. Pyrolysis reaction must be carried out before the end product can be obtained. Also, economical problems arise from the use of expensive reactants and increased installation cost.
There is a need for the commercially advantageous manufacture of perfluoropolyether while overcoming the above-mentioned problems.